Given the root of a binary tree and two integers p and q, return the distance between the nodes of value p and value q in the tree.
The distance between two nodes is the number of edges on the path from one to the other.
Solution
求树上两个点之间的距离。很经典的做法就是求出 \(LCA\)，然后分别求出两点分别到 \(LCA\) 的距离即可
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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
private:
TreeNode* LCA(TreeNode* rt, int p, int q){
if(!rt) return NULL;
if(rt->val==p || rt->val==q)return rt;
TreeNode* leftrt = LCA(rt->left, p,q);
TreeNode* rightrt = LCA(rt->right, p, q);
if(leftrt&&rightrt)return rt;
if(!leftrt && !rightrt)return NULL;
return leftrt?leftrt:rightrt;
}
int get_depth(TreeNode* rt, int v, int dep){
if(!rt) return 0;
if(rt->val==v) return dep;
return get_depth(rt->right, v, dep+1)+get_depth(rt->left, v, dep+1);
}
public:
int findDistance(TreeNode* root, int p, int q) {
TreeNode* lca = LCA(root, p, q);
return get_depth(lca,p,0)+get_depth(lca,q,0);
}
};